The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Driven by the need for smaller size, reduced power consumption, and enhanced efficiency and functionality, future ultrahigh resolution display technologies require the development of submicron-scale, high-efficiency, multicolor light sources monolithically integrated on a single chip. The challenges of organic light emitting diodes (OLEDs) for these applications include limited lifetime of organic materials, relatively expensive manufacturing process, low efficiency and brightness, and poor stability. Moreover, it has remained difficult to achieve micro-scale or nano-scale devices using organic materials.
GaN-based quantum well Light Emitting Diodes (LEDs) are bright, stable and efficient, but usually only emit in one color. It has also remained difficult to achieve efficient deep green and red emission using GaN-based quantum well LEDs. Additionally, there is no established technology to spatially vary Indium (In) compositions in quantum wells to achieve multicolor emission on the same substrate.
Recent studies have shown that such critical challenges can be potentially addressed by using InGaN nanowire structures. Nanowire LED heterostructures exhibit low dislocation densities and high light extraction efficiency. GaN-based nanowire LEDs and lasers operating in the ultraviolet (UV), blue-green, and red wavelength range have been demonstrated.
Furthermore, it has been shown that multicolor emission can be achieved from InGaN nanowire arrays monolithically integrated on a single chip. It is further envisioned that display technologies based on pixels of single nanowire LED arrays integrated on the same chip represent the ultimate light sources for the emerging three-dimensional (3D) projection display, flexible display, and virtual retinal display (VRD) technologies. The radiation pattern and emission direction can be well-controlled and tailored by the columnar structure of each single nanowire, which is essential to achieving ultrahigh definition displays. In addition, pixels of single nanowire-based LED arrays can be much more efficient in heat dissipation and can operate at extremely large injection current levels. Critical to these technology developments is the demonstration of full-color, tunable light sources including LEDs and lasers using single, or a few nanowires on the same chip. This requires a precise tuning of alloy compositions in different nanowire structures and that these compositional variations should be ideally introduced in a single growth/synthesis step.
It was previously demonstrated in prior art that it was possible to produce multiple colors by varying the diameters of nanowires that are in a densely packed array in a one-step selective area epitaxy, that is, without changing the global growth parameters of the crystal growth process and system. However to make arrays, on the same chip, that emit in multiple colors the process had to be done in a multi-step selective area epitaxy process. This approach, as used in the fabrication of densely packed nanowire arrays, takes advantage of the shadowing effect of neighboring nanowires to alter the InGaN composition in densely packed array of nanowire structures. To date, however, little is known about the mechanism on how to controllably vary the alloy compositions at the single nanowire level without changing the global growth parameters. The monolithic integration of multicolor, single nanowire LEDs on the same chip has thus remained elusive.
It is desirable, and extremely challenging, to be able to fabricate a semiconductor-based light-emitting photonic device that has all the following attributes. Successful realization of a product that truly has all the characteristics which are listed below has been one of the holy grails of the photonics industry for several decades now. These devices have many applications in various products such as for example high-resolution and true-color displays that are used in applications such as computer screens, mobile phone screens, and high-definition televisions.